The present invention relates to a molding system. More particularly this invention concerns a dual-speed method and apparatus for closing a blow mold.
It is standard as described in U.S. Pat. No. 5,720,918 to close a two-part mold by first moving the mold halves together at a relatively high speed until they touch, then pressing them together with much greater force during the subsequent filling, blowing, and curing steps of a blow-molding operation. The mold halves are carried on respective support plates that can slide along a base. A double-acting light-duty hydraulic cylinder extends between the support plates, typically below the base, and serves for the fast mold-closing operation. Further heavier-duty cylinders mounted right on the mold plates are employed to apply the much greater force needed to clamp the mold halves together during the filling of the mold and curing of the molded article.
Such an arrangement is fairly complex. There are two separate actuators that must be controlled independently and in general the system is quite complicated.
It is therefore an object of the present invention to provide an improved mold-closing system.
Another object is the provision of such an improved mold-closing system which overcomes the above-given disadvantages, that is which is fairly simple in construction and operation.
A mold system has a pair of mold halves movable toward and away from each other, a threaded spindle coupled to one of the mold halves, and a nut threaded on the spindle and coupled to the other of the mold halves. A brakable spindle motor is connected to the spindle and operable to rotate the spindle in the nut and a nut motor separate from the spindle motor is connected to the nut and operable to rotate the nut on the spindle. In a first mold-closing stage the spindle motor is operated to rotate the spindle in the nut and move the mold-halves rapidly toward each other. Thereafter in a second and subsequent mold-clamping stage the spindle motor is braked and the nut motor is operated to rotate the nut on the spindle and press the mold halves against each other.
Such a system is quite simple. It uses a straightforward spindle/nut assembly for both the high-speed low-force closing operation and the low-speed high-force clamping operation. According to the invention the spindle motor is a high-speed low-torque motor and the nut motor is a low-speed high-torque motor, either electric or hydraulic. The use of two separate motors each built for its specific task means that two relatively small devices can be used.
According to the invention in the mold-closing stage of the nut motor is braked. Thus all of the movement in this stage is the responsibility of the spindle motor. Normally according to the invention braking of the nut motor is stopped shortly before the spindle motor is braked, whereupon the nut motor takes over to continue the movement but at a lower speed and greater torque. It is also possible in accordance with the invention to operate the nut motor in the mold-closing stage to rotate the nut on the spindle while the spindle motor is operating, thereby using both motors for the closing stage.
During filling of a cavity of the mold halves both of the motors are shut down and braked to lock the mold shut, allowing them to cool. Furthermore according to the invention the nut and spindle are interconnected by recirculating balls. The system has according to the invention a base on which the mold halves are displaceable horizontally and a pair of first-class levers pivoted on the base and each having one end connected to a respective one of the mold halves and another end. One of the other ends is connected to the nut and the other of the other ends is connected to the spindle. The spindle motor is carried on the one of the other ends and the nut motor is carried on the other of the other ends.